A support unit for partition walls typically for the load compartment of isothermal vans, comprising at least one carriage (3) slidable along a respective longitudinal guide (1) fixed to the roof of the load compartment, and provided with a transverse shaft (13) for supporting and hinging a partition wall (11), which can rotate between two end positions, which are vertical and virtually horizontal; said at least one carriage is provided with a slidable vertical latch which is constantly urged elastically towards a rack carried by the respective guide; between said wall and said latch there is interposed a controlling linkage system of variable geometry which along the two opposite terminal arcs of a complete rotation of the wall is insensitive to the wall movement, whereas along that arc of the rotation extending between the preceding arcs it causes release of the latch.